The present invention relates generally to cutting devices, and particularly to a power-lever cutting device, such as a pruner.
Cutting devices that are used to cut or prune branches and limbs from various plant materials typically are hand held and have elongated members or handles disposed for cooperative engagement about a pivotable joint. In particular, pivoted tools, such as pruning snips or shears generally comprise two elongated members typically made of stamped or forged metal or other suitable metal disposed for cooperative engagement about the pivotable joint. Typically, each member includes a jaw in the front end portion thereof, an opposing tang, and a pair of handles connected to the jaw and tang.
In the case of conventional pivoted pruners, when cutting a branch, the cutting force applied to the branch is constant during the cutting process. Typically, the cutting force need is at its greatest is a little after the cutting blade reaches the middle of the branch or object being cut. The typical conventional pruners have a simple scissors-like mechanism with one rivet connecting the handles and the cutting jaws of the pruner. In such construction, the cutting power of the tool, at any moment of the cutting process, depends only on the force of the hand squeezing the handles at that same time. It is not unusual to have longer handles to exert a greater moment force about the pivot point in order to increase the cutting power of the cutting blades. However, such longer handles are cumbersome and difficult to use with one hand and the force is constant during the entire cutting process, regardless of the resistance being experienced by the blade.
In the known scissors-like pruner construction, typically the index and middle fingers are partly unemployed during the cutting process. Since those fingers are typically the closest fingers to the pivot point of the cutting tool jaws, their power cannot generate much torque about the pivot point. The distance moved by those two fingers is also short in comparison to the ring and little fingers of the same hand gripping the handles of the pruning tool.
In conventional pruners, as described above, the peak power of the cutting stroke is achieved as the blades pass through the middle portion of the branch or limb being cut. However, as the cutting stroke continues through the branch, not as much power is needed resulting in a relatively strong impact at the end of the cutting stroke when the resistance presented by the piece being cut is reduced. Such strong impact has been described as being a xe2x80x9csnap-effect.xe2x80x9d
Various attempts have been made to address the problem of the snap-effect as well as maximizing the power exerted by all the fingers of the hand operating the cutting device. For example, the assignee of the present application markets a pivoted hand tool utilizing a rack and pinion mechanism between the elongated members of the tool to increase the cutting force applied by the jaws to the object being cut. Another embodiment of the present assignee""s pivoted hand tool provides an elongated flexible element and groove formed in a handle of the tool at a distance from the rotation axis of the handle. However, both of these two devices are complex and difficult to assemble and manufacture. Other devices utilize longer handles to provide the necessary force or a combination of springs or rocking arms pivoted between a fixed jaw and a movable jaw with the rocking arm guided through a groove and engaging various notches to change the force applied at the jaws. Such mechanisms do not distribute the force across the fingers or hands operating such devices nor do they minimize or eliminate the snap-effect at the end of the cutting stroke.
Thus there is a need for a cutting device, such as a pruner, that provides linear movement of the handles toward each other during the cutting process. There is also a need for a cutting device that will maximize the force exerted by all of the fingers of an operator""s hand during the cutting stroke. There is an additional need for a cutting device or pruner that utilizes variable cutting power during the cutting stroke of the blade and jaw of the cutting tool. There is a further need for a cutting device or pruner that will minimize or eliminate the xe2x80x9csnap-effectxe2x80x9d at the end of the cutting stroke.
The present invention increases the output force of a cutting device or pruner (i.e., the force applied to the piece being cut) in a variable manner as the blade and jaw travel through the piece being cut. The present invention does not rely on longer handles to increase the moment about a pivot point to increase the power during the cutting process. With the present invention, more power is used to rotate the blade instead of modifying the force about the rivets holding the blade and jaw together. A power lever coupled to the two elongated members or handles of the present cutting device cause the handles to move towards each other in a linear fashion, the effect of which is to maximize the force being exerted by all the fingers of the operator""s hand.
The power-lever cutting tool in accordance with the invention comprises a metal plate having a central aperture, a forwardly extending blade and a rearwardly extending tang having a second aperture offset from the central aperture, a first elongated member comprising a first handle terminating at a distal end by a jaw, a second elongated member comprising a second handle and a power lever having a first end and a second end. The first and second elongated members are pivotally connected to the plate at the central and second apertures by couplers, respectfully. Further, the first and second elongated members are pivotally connected each to one end of the power lever so that the second elongated member moves linearly toward the first elongated member for a linear movement of the blade and jaw in response to pivotal movement of the first and second handles about couplers in the central and second apertures, respectively. The second elongated member can include a mounting finger configured to engage one end of the power lever.
According to another aspect of the present invention, a pruner comprises a first elongated member and a second elongated member coupled to a metal plate and a power lever. The metal plate has a central aperture, a forwardly extending blade and a rearwardly extending tang having a second aperture offset from the central aperture. A jaw is mounted on the first elongated member. The power lever has a first end and a second end. A first coupler pivotably mounted in the central aperture and coupling the first member to the plate, with a second coupler pivotably mounted in the second aperture and coupling the second member to the plate. The power lever is coupled to the first and second elongated members by a third coupler pivotably coupling the first end of the power lever to the second member and a fourth coupler pivotably coupling the second end of the power lever to the first member. The power lever forces the second member to move linearly toward the first member for pivotable movement of the blade and jaw in response to linear movement of the first and second members. In one embodiment the pruner includes a mounting finger formed on the second elongated member and configured to engage one end of the power lever.
Another embodiment of the present invention is a cutting device comprising a means for cutting having a central aperture, a forwardly extending blade and a rearwardly extending means for mounting having a second aperture offset from the central aperture. The first means for holding comprising a first handle terminating at a distal end by a jaw, a second means for holding comprising a second handle and a means for leveraging having a first end and a second end. The first and second means for holding are pivotally connected to the means for cutting at the central and second apertures by means for coupling, respectfully and further pivotally connected each to one end of the means for leveraging so that the second means for holding moves linearly towards the first means for holding for pivotal movement of the blade and jaw in response to the linear movement of the first and second means for holding. One aspect of the present invention provides the second means for holding includes a means for resisting configured to engage one end of the means for leveraging.